Problems of hydro-electric design in mixed thermal–hydro-electric systems

Abstract

The paper deals with some of the problems which arise in the planning and development of a system comprising both thermal and hydro-electric plant. In general, when thermal plant predominates it is considered desirable to develop hydro-electric power with the greatest installed capacity the system can absorb in conjunction with the available amount of energy. Practical limitations to low-load-factor operation are discussed. The effects of the introduction of low-load-factor hydro-electric plant on system operation and on the overall fuel consumption of the thermal plants are examined. New circumstances which cannot readily be forecast may later make desirable a change in the design load factor of some of the hydro-electric plants, and the paper stresses the advantage of having, where possible, flexibility in the initial design to enable such changes to be made. Where circumstances permit, consideration of the use of pumps, and especially reversible pump-turbines, is recommended as a means of augmenting storage capacity and either increasing the firm annual load factor or permitting increased installed capacity. The basic economics of the pumped-storage scheme are explained and an example illustrating the flexibility which is possible in planning such an installation is given in the Appendix. The paper discusses the effect on hydro-electric development of the possible ultimate replacement of coal and oil by nuclear fuel in thermal plants, and it is concluded that hydro-electric plant is likely to continue to be advantageous for peak-load operation and that there is no justification for any postponement of long-term investment in hydroelectric works on account of the advent of nuclear power. The effect of rising prices is also discussed, and a general survey is given of present practice in the design of hydro-electric machines. Transmission practice and problems are briefly reviewed as an integral part of hydro-electric design. In conclusion it is pointed out that differences of opinion between thermal and hydro-electric engineers may arise because of inadequate mutual understanding of the inherent characteristics of the two types of plant and of the problems of combined operation. The design of hydro-electric projects in a mixed system must be based, not only on the hydrographical and civil engineering data, but on a comprehensive study of all the many factors involved.